By Mike Wallace
Updated Mar 24, 2022
A snubber is a circuit element that mitigates voltage spikes caused by sudden changes in current. These transients can damage components and produce arcing or sparks. An RC snubber, composed of a resistor and a capacitor in parallel, is one of the most common solutions. To design an effective RC snubber, you must consider the specific switch and its switching frequency before selecting component values.
Confirm that the electrical switch is in the "Off" position and that it is connected to the power source. This ensures a safe starting point for measurements.
Place a voltmeter across the input and output terminals of the switch. Flip the switch to the "On" position and record the voltage reading. This value represents the voltage the snubber must withstand.
Consult the switch’s datasheet to determine its maximum current rating. This specification is critical for sizing the resistor component.
Divide the measured voltage by the maximum current to obtain the minimum resistance required. For example, if the voltage is 160 V and the current rating is 5 A, the resistor must be at least 32 Ω.
Find the switching frequency (in hertz) from the circuit documentation. For instance, a 50 kHz switching rate is common in power‑converting circuits.
Use the formula C = 1 / (V² × f), where V is the voltage measured in Step 2 and f is the switching frequency. For a 160 V voltage and 50 kHz frequency, the calculation is:
C = 1 / (160² × 50 000) ≈ 780 pF.
Follow these steps to design an RC snubber that reliably protects your circuit from harmful transients.
